1. Field of the Invention
The present invention relates to a movement distance measuring apparatus. More particularly, the present invention relates to a movement distance measuring apparatus mounted to a portable terminal.
2. Description of the Related Art
In recent years, as interest in personal health has increased, apparatuses that measure movement by determining the number of steps or by measuring movement distances have been developed. The apparatuses are occasionally mounted to mobile communication terminals which are typically carried by their users.
To estimate a step length of a pedestrian, such a measuring apparatus uses a walking frequency and an acceleration variance that reflect the characteristics of a step length change according to a step pattern. FIG. 1A is a view illustrating a relation between step lengths and walking frequencies, and FIG. 1B is a view illustrating a relation between step lengths and acceleration variances. Referring to FIGS. 1A and 1B, it can be seen that the step lengths have linear relations with the walking frequencies and the acceleration variances. Therefore, a step length can be represented by a linear combination of the two parameters of walking frequency and acceleration variance as in equation (1) below.Step length=a1WF+a2AV+b  (1)
In equation (1), a1 and a2 are respectively weights of a walking frequency and an acceleration variance, b is a constant term, WF is a walking frequency, and AV is an acceleration variance.
Therefore, since a walking frequency and a variance value of an accelerometer output when one step is generated can be calculated, the total movement distance can be calculated as in Equation (2) below by summating step lengths when several steps are generated.
                              Movement          ⁢                                          ⁢          distance                =                              ∑                          i              =              1                        n                    ⁢                                          ⁢                                    (                                                                    a                    1                                    ⁢                  W                  ⁢                                                                          ⁢                  F                                +                                                      a                    2                                    ⁢                  A                  ⁢                                                                          ⁢                  V                                +                b                            )                        i                                              (        2        )            
In equation (2), n is the number of detected steps, and a1, a2, and b are weights in a linear combination of a walking frequency and an acceleration variance and are calculated by a linear regression.
As the use of portable terminals has grown, a user will occasionally mount a movement distance measuring apparatus to the portable terminal for convenience. However, in the case in which the portable terminal including the movement distance measuring apparatus is mounted at the waist of the user or is located in the user's pocket as illustrated in FIG. 2, a1, a2, and b, which are step length estimation parameters, are different. Accordingly, a step length estimation error is generated due to the mounting position. Therefore, a method for recognizing a mounting position so as to use a parameter coefficient suitable for the mounting position of the movement distance measuring apparatus is necessary.
That is, a conventional movement distance measuring apparatus does not address a change of an algorithm that is necessary according to a mounting position of the movement distance measuring apparatus. Because the conventional movement distance measuring apparatus cannot discriminate between mounting positions, an error becomes large and the measurement can not be properly performed since the movement distance and the movement are calculated by the same algorithm.